Electron storage device with grid control action



JUY 4, 1950 .1. A. RAJCHMAN $513,743

ELECTRON STORAGE DEVICE WITH GRID CONTROL ACTION Filed Jan. l5, 1947 3 Sheets-Sheet l Zhwentor July 4, 1950 J. A. RAJCHMAN M3343 ELECTRON STORAGE DEVICE WITH GRID CONTROL ACTION Filed Jan'. 15, 194'? Snnentor fd/2 Rayo/maiz (Ittorneg 5 Sheets-Sheet 2 july 4, i959 J. A. RAJCHMAN 2,53743 ELETRoN STORAGE DET/TCE WITH GRID CONTROL ACTION Filed Jan. 15, 1947 3 Sheets-Sheet 3 F/,esr meat-7.57

l v Al/ A/ A! l fyi-774195.57

l l Il l V l :Snuentor Gttomeg atented July 4, 195@ UNITED S ,nur

E 'r F ELECTRON STORAGE DEVICE WITH GRID CONTROL ACTION Jan A. Rajchman, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Claims.

This invention relates to electron discharge devices of the type in which an elemental area of a target electrode is charged to one of two predetermined potentials so as to constitute a memory element for use in electronic computers, and in particular to an improved method of and means for indicating to which potential the memory element has been charged. In a copending application of J. A. Rajchman, Serial No. 665,031, led April 26, 1946, which is now U. S. Patent No. 2,494,670 granted January 17, 1950, an electron discharge device of the storage or memory type has been described.

In accordance with the aforementioned copending application, one or more horizontal and vertical grid networks are employed to direct a stream of electrons at a selected elemental area of a target electrode. The target electrode consists of an insulating secondary emissive material which may be coated on a metallic signal plate or otherwise constructed in such a manner that the dielectric surface is capacitively coupled to the` signal plate. By applying suitable potentials to the signal plate while controlling the flow of electrons to the selected target area, it was shown in the copending application referred to above that the dielectric element under bombardment may be made to assume either one of two potentials which are stable under continuous electron bombardment. By conditioning successively selected elemental target areas to one or the other of the two possible stable conditions, the device may be made to store or remember the information which has been applied to it. The device has utility in connection with computing systems utilizing the binary system of counting wherein one of the two stable conditions represents the ligure 0 and the other stable condition represents the figure 1, or any other system of counting in which the numbers are represented by coded combinations of the two conditions. It is thus possible to store in a device of this nature a series of conditions each representative of a number to be used in the process of computation.

In the original arrangement the system employed for subsequently determining the existing condition of a selected elemental area also utilized the signal plate. As a result it was dicult to separate signals produced by the application of pulses to the signal plate for storing information from the signals which were indicative of the condition of the memory elements. In addition, since the indicating system responded to the displacement current required to charge or discharge the capacity of the memory element, the time required to determine its condition was not as short as may be desired.

A modied method of and apparatus for determining the condition of a memory elementwhich utilizes the light emitted from fluorescent material deposited on the surface of each elemental area has been described in copending application of J. A. Rajchman, Serial No. 720,876, filed January 8, 1947, now Patent No. 2,442,985, dated June 8, 1948. This system has certain advantages and permits the condition of the elemental area to be determined independently of the signal plate. However, in order to produce light of suicient intensity to be useful, it is necessary to cause the electrons to strike the uorescent surface at a high velocity. This requirement makes it necessary to maintain the dielectric surface at a high potential. Since the dielectric surface of the target is continuous and the selection of elemental areas is effected by causing electrons to impinge on separate adjacent regions, it will be appreciated that as the size of each region\ and the spacing between adjacent regions is reduced, for the purpose of providing the largest possible number of memory elements in a given area, the problem of preventing leakage from a highly charged elemental area to an adjacent area which is at cathode potential becomes increasingly diicult. The leakage factor determines the time during which the device will maintain its memory or charge in the absence of electron bombardment. Consequently, in order to reduce leakage between adjacent elements, it is desirable to charge the elemental areas to the minimum Voltage possible. The two requirements mentioned above indicate opposite operating procedures.

It is the primary object of this invention to overcome the disadvantages of the earlier systems by separating the indicating and storing functions.

In brief, the objects of this invention are accomplished by providing one or more holes in the dielectric surface which constitutes each memory element with corresponding holes in the signal plate, and also providing a second target electrode so that at least some of the electrons directed toward the selected area will pass through the first target'electrode and impinge on the second target electrode, provided the potential of the dielectric area is sufficiently positive. If,

however, the dielectric surface is at cathode potential it will act as a control grid and will block the passage of electrons. Consequently, the electron flow through the storage element, that is, through the rst target electrode, depends upon 4the condition of the memory element. The electrons passing through the first target electrode may then be collected at the second target electrode and used to indicate the condition of the memory element without interfering with the operation of the element itself.

It is therefore a further object of this invention to provide animproved method and means for indicating the condition of the memory elements of an electron storage tube by means'A of an electron current which is controlled bythe potential of the element and which is therefore indicative of its condition. f y

Itis a further object of this invention to provide alternate forms for the first and second target electrodes.

The proper control and direction of the elecplates and their purpose is to direct electrons emitted from the cathode toward the grid and other electrodes of the tube so that they approach the second accelerating electrode 29 in paths substantially perpendicular to its surface.

The second accelerating electrode 29 is provided to cooperate with the focusing electrodes and' to direct the electrons' in the desired direction. This electrode is preferably a stamped metal plate having a large number of small cirv cular apertures therein. These perforated plates may be ofthe order of .040 inch. When four lidentical segments vare employed this electrode may be formed of a' single sheet, bent to form a `substantiallysquare enclosure.

trons emitted from the cathode requires theirv i successive passage through a plurality of gridlike or` apertured electrodes. -IfY conventional practicesare followed inthe construction of the various 4electrodes great difficulty will be encountered. in positioning them so that theirfapertures areinregister. ject .of this invention, an improved-constructional arrangementy vis provided in which perfora-ted `Inaccordance with a further ocf metal plates-are employed'which may Iloefstaclred in .spaced parallel relationship on *insulating ceramic or. glass'rods to provide a 'rigid unitary structure which may be manufactured morer readily than previously known arrangements.` Additionalhinsulating rods passi-ng through" the perforatedplates'may also be used to space the wresof the selecting grid networks.`

Thenovel features that are considered'char-` acteristic of this invention Yare set lforth with particular-ity in the appended claimst The invention yboth as to its organization and method v of operation, as well 'as additional objects andl ,w

circuit connections for a tube of the type herein illustrated, v

Figs. l to 8, inclusive, are sectional views of a portion of modified forms which may be'used for I the iirst target electrode, and

Figs. 9 and 10 are sectional views of modified forms of second target electrodes.

Referring to Figs. `1, la and 2, inv its simplest form the'electron discharge storage device inaccordance with this invention is constructed as follows: Y A* An elongated cylindrical vcathode'l is centrally located along the axis of the tube which is' enclosed in an evacuated envelope 22. Surroundingthe cathode is a lfirst accelerating electrode 23 which consists'of a spiral of ne wire and may be mounted on four supporting rods suitably1 anchored in the base of the tube. The electrode structure may consist of from one to fouridentical sections, only one of which has been illusfA trated. Extending radially from' the cathode and in register with the yfour supporting rods of the rst accelerating electrode are two focusing electro'des 25 and 2l. These electrodes are metallic Next .inorder beyond the second accelerating electrode is the horizontal control grid network 3l. This network consists of a plurality of indi vidually insulated" strips or conductors lying spaced fromfand-para-llel tothe second accelerat ing' electrode and-positioned between the horizon'talfrowsfof apertures in the latter electrode,-as best illustrated in- Fig. 2. In the view lshown in Fig. 1, one such electrode is visible. Next in orderis a shield electrode 35 which'consists of a perforated metal plate of approximately the same size as one face of the secondaccelerating electrode 29, and mounted parallel thereto with the holes of the'two electrodes in register.

Following theshield electrode 35 isthe vertical control grid-network 3l which consists'of a plurality of strip conductorssimilar to those of the horizontal ygrid network but positioned at right angles thereto and parallel vto Vthe other electrodes; Although not shown herein, the individual'wires of the horizontal and vertical -control gridnetworks are to be vseparately connected for individual AeX-citaftioninaccordance with the teaching of the copending application Serial No. 665,031. Methods for effecting complete control ofy theele'ctron streamutiliz'ing a number of eX- ternal/leads which is lessthan the number of individual grid wires have been described and claimed.y in a copending application of J. A. Rajchman, Serial No. 702,775, filed October 11, 1946, and the application` of George W. Brown, Serial No. 694,041; filed August 30, 1946; which is assigned to a common assignee.

It is to be understood 'that the particular arrangement employed for directing the electrons toward the selected elemental `area on a mica spheet"59 of a'rst 'target' electrode 551 isV not, as

such, a part ofthepresent invention, and any ofthe arrangements `described in the copending applications referred to above may be employed.

Following' the vertical controlA Ygrid network therel is a collectorelectrode 55- whichY is also a perforated metal plate similar in size yand con struction. to thoseemployed for the shield Yand second-accelerating electrodes.r The holes in the collector electrodeare valso Ain register with' the holes ofthe preceding electrodes.

Next in order is the rst target electrode '51.

This electrode has, essentially,'two parts and two' sheet 59' andcapacitively coupled. toK all points,`

thereon is a metal"capacity plate El. This plate may again be a perforated metal sheet of 'the same size as that employed for the collector and .the other electrodes.

Finally, the second target electrode 63 is mounted parallel to and adjacent the first target electrode. In its simplest form this electrode may comprise merely a solid metal sheet 62, although modied forms will be discussed subsequently.

An important feature of the present invention resides in the unique constructional arrangement employed to support the various electrodes. The inner and outer electrodes (excluding the cathode and rst accelerating electrode) are preferably supported rigidly by vertical supporting rods embedded in the glass base or supported between two mica sheets in accordance with conventional practice, while all the other electrodes are supported by suitable insulating rods which pass through aligned apertures along the edges of these electrodes. For example, the second accelerating electrode 29 is supported at its outer edges, or at the corners in case four identical sections are employed, by supporting rods such as 3l) and 32, while the target plate 62 is supported at its outer edges by two supporting members @il and 36. Four insulating tubes or rods, 38, di), 2li and 2t, are passed through the apertures in the four corners of the two electrodes. These rods provide the support for all intermediate perforated plate electrodes. The electrodes may be held in spaced parallel relation by means of insulating spacers which are placed around the rods between the electrodes and the rod may be threaded and provided with nuts at each end to hold the whole assembly together. Alternatively an insulated bolt may be passed through the supporting tube for the same purpose, as shown. All the apertures in the perforated plate electrodes will then be held rigidly and permanently in register. Since standard, identical perforated plates may be employed the manufacture of an otherwise complicated structure has been greatly simplied.

The operation of the device including the selection of the individual storage elements, the release of secondary electrons by the dielectric surface of the first target electrode, and the method of conditioning the storage element to one or the other of the two stable conditions is as described in the earlier applications referred to above, and need not be described herein in greater detail. The resulting electron ilow under the two possible conditions has been illustrated in Fig. l. Assume that the aperture or window dened by vertical electrodes 39 and 4l, together with the two corresponding adjacent horizontal electrodes, has been opened by the application of suitable opening potentials to the four wires of the two grid networks. This condition is indicated by the sign on the two vertical grid conductors Se and el. Assume further that the storage element, that is, the area of the dielectric 59 in register with the window so defined, has previously beenv set at cathode potential. Electrons passing through the open window and the aligned aperture in the positive collector electrode 55 will be turned back toward the collector and will not impinge on the surface of the storage element. This is because the storage element is at cathode potential and the collector electrode is at approximately 300 volts. Of course a few electrons may strike the storage element from time to time if its potential tends to increase. However, as pointed out above, this is merely the stabilizing action which tends to maintain the element at cathode potential. As a result, no electrons pass through the small aperture 56 and no electron current flows in the second target electrode V62.

The other condition is also illustrated in Fig. l. Assume that the window dened by vertical grid wires l5 and lil, and the cooperating horizontal grid wires, has been opened and that the storage element in register with this window has previously been charged to collector potential. In this case electrons will now through the window and strike the dielectric surface of the storage element at sufficient velocity to release secondary electrons. These are collected by the collector electrode, which is maintained at a positive potential. In addition, certain electrons of the impinging stream pass through the aperture 58, centrally located in the storage element and strike the second target electrode 62, which is maintained at a much higher potential. The resulting electron current canthen be measured or used to produce an output indication by a suitable connection to the target electrode 62.

The purpose of the negatively biased capacity plate is two-fold. First, the capacity plate is used to condition the storage elements in the manner discussed above. Second, due. to its negative potential, the capacity plate acts as a shield so as to insure that the electric field produced by the highly positive accelerating electrode does not extend through the small apertures in the dielectric rst target electrode 59. The negative eld assists the storage element in turning impinging electrons back towards the collector electrode when the element is at cathode potential, but is not suniciently negative to prevent the passage of electrons when the element is at collector p0- tential.

The electrical circuit `connections for the device illustrated in Figs. l and 2 are shown in Fig. 3. The cathode El is preferably connected to ground while the focusing electrodes 25 and 2l, the accelerating electrodes 23 and Z9, the shield electrode 35, the collector electrode 55 and the second target electrode are all connected to a suitable source of D. C. potential the approximate values of which are indicated in Fig. l. This source may, for example, be provided by a battery l2 and a resistance voltage divider di?. The control circuit for applying opening potentials to the horizontal and vertical grid network conductors is indicated by device dii. The conditioning pulse input is applied to terminal i8 which is capacitively coupled to the capacity plate 6l by means of a condenser 5G. Output is taken from terminals 54 across the load impedance 52. i

The collector electrode 55 may be modified as shown in Fig. 4 by the addition of a fine mesh screen of copper lil, the purpose of which is to shield the first target 59 from the wires of the vertical control grid 3l, so that the field conditions prevailing at the surface of the first target 5S depend only on the potential of the collector 55 and are independent of the switching potentials applied to electrodes 3l.

An enlarged View of an alternative form of the rst target electrode 5l is shown in Fig. 5. The capacity plate El and the perforated mica sheet 59 which constitutes the storage elements are employed as before. In addition, an auxiliary shield electrode (it, consisting of a perforated metal sheet similar to that employed in the other electrodes, is placed against the inner surface of the mica. The purpose of this auxiliary electrode, which may be biased to a potential of volts, is to provide a, definite potential between adjacent storage elements 4inorder to minimize leakage. If, for example,2the dielectric surfaceof element 66 (Figi-5). isvatcollector potential and the. surface ofthe-adjacent storage element G8 is atcathode-potential, there wouldbean unduly large potential gradient between them if the intermediary region assumed the potential' of one or the other of these elements 66 and 68,!a condition which would-be conducive to promote a leakage current. However, by creating points ata potentialintermediate between the cathode'and collector potentials, Whichis -accomplislied'by the auxiliary electrode til, the potential gradient tending to. cause leakage between elements -66- and 68 isminimized. While there may be some-ohmic leakage by 'conduction on.thea-dielectricsurface itself, leakage may also Abe effected by the movementof stray secondary .electrons \or deflected primary veleotrons-from one-element to another. The auxiliary electrode t4 yisparti'cularly effective in preventing leakage ofthe latter type.

A further alternative form which-may be employed in the construction of the first. target electrode l is shown in Fig. 6. In lthis case'the capacity plate lill' consists of two perforated metal sheets of the type previously employed between which is clamped a fine mesh 'i2 of copper wire having from 10'() toe'i) wires per linear inch. Alfter assembly this ielectrode is coated with an insulating dielectric material which is secondaryemissifve. |The coating material then constitutes theistorageelectrode, the surface of which is impinged by the electrons. The advantage -of this arrangement -is ...that very fclose capacity coupling can be providedbetween the surface of the dielectric and thecapacity plate. As before, the capacity plate will normally be biased to a potential of 50 volts, while the conditioning p-ulsev is superimposed-on the fixed bias as in the previous case. When the storage element, that is, the dielectric surface, is `at cathode potential, the electrons will not pass through 'the^screen. However, when the surface is at collector potential, those electrons which strike thedielectric surface will release secondary electrons to' maintain the potential in a 'stable condition, 'while some will pass through the screen to the'second vtargetelectrede. An additional auxiliary electrode vcornprisin'g a perforated metal sheetma'y--be placed between the iirst and secondltarget'electrodes in order to vneutralize the fieldfrom the second `target electrode. This will insure that theelectric field at the'centerfof the Wire'mesh will not'exceed cathode potential.

In the embodiments illustrated above, in order for the storage elementto function as a control grid and to prevent the-passage therethrough of electrons when it is at cathode potential, it is desirable that as great an area'of the element as possible be brought to* cathode potential. When mica is used, the'sides of the cylindrical hole 58 (see i, la orti) are parallel to the path of thel electrons and will Lnot normally be struck by any electrons. Consequently; cathode potential will exist only at the inner surface 'of the dielectric and will not extenddownwardly into the hole, Control'can be improved by'pi'o'viding an arrangement such that tlieentire surface of the dielectric is exposed to the electron stream'. 'This maybe accomplished, for example, as illustrated in Fig. '7. The small aperture in the dielectric surface is made conical in shape with its larger 'diameter facing the cathode. Since such construction would Abe difficult 'to accomplish. with mica, land also .to illustrate an alternative structure, in Fig'.

, 8 7 theA rstlta'rget electrode comprisesa metal capacity plate vlil .having conical perforations which may readily be machined in a metal plate. The electrodeis then treated to .deposit on its surface a .dielectric material of high secondaryemi'ssive characteristics. For examplathis may be'v accomplished. .by kanodizing .aluminum in accordance with conventional practices or covering the metal surface with silica or a suitableenamel having .the desired characteristics. The entire surfaceof the .aperture will then be exposed to the -electron' 'stream and a strong positive eld will be. created, and in one case, while the entire surface lwill be maintained at cathode potential in the other case. This design will ensure positive control-fof the passage of electrons through the Jholes.- lThe conical shape also ensures that thel'collect'oriield will leak sufficiently into the aperture for. an equipotential to follow the contourof. the aperture and to create, consequently, a uniform.1potential throughout its entire surface. Auxiliary electrodesto properly form vthe electric field and to minimize the yfield. between adjacent v, elements-may be placed on either or both sidesk of the .first .Ltarget electrode. v

As pointed out above, it is desirable that the entire .surface of the aperture be maintained at collector or cathode potential in order to insure adequate control action of the storage element. The .methods .outlined above accomplish this by insuring uniform electron bombardment over the entire surface and va uniform potential along the entire surface. Since in the preceding cases the dielectric surface Vof 4the aperture is nonconducting, the potential of one point can be different from the Vpotential of an adjacent point if the above .precautions are not observed. An alternate method of insuring uniform potential over the entire surface of the aperture is illustrated in Fig. 8. fn this case the irst target comprises a rmetal capacity vplate ti of the type previously utilized, in whicha small metallic sleeve 'I4 is inserted in the metal capacity plate and suitably insulated therefrom by means of glass or ceramic sleeves '5.6. These metal .sleeves are generally funnelshaped, having their larger diameter toward the, electron stream.' The sleeves are in register with the .corresponding apertures in the adjacent collector .electrode and will be bombarded by electr-ons when the associated windows are open. Since .most metals .are secondaryemi-ssive these .sleeves will function as storage elements in .a manner identical to the dielectric surfaces described above. However, since they are' conductive, the potential at all .points must necessarily beidentica'l. vBy applying conditioning pulses tothe capacity plate as before, and controlling the electron bombardment, 'the potential of each metal sleeve may be set ateither cathode potential orcollector potential. In the former rcase no electrons willpass through the metal sleeve while in the latter case some of the impinging electrons will .passthrough and strike the second target electrode. Asimilar result can be obtained valso by using the .construction of Fig. 7 fand. evaporating metal into the conical aperture through an appropriate. mask.

The second target electrode t3 in Fig. 1 was a solid metal plate. incertain cases it is desirable to Vproduce a light indication to show visually the condition of the-element. An alternative form of second target electrode suitable for this purpose is illustrated in Fig. 9. In this case the electrode structure iscomposite and comprises a perforated metal yplate 6l of the type utilized for the other electrodes. This electrode isplaced adjacent and preferably in contact with a fluorescent target which may consistl of a, transparent base 65, such as mica, or glass, on the surface of which there is a coating of fluorescent material 18. Electrons which pass through the rst target electrode, as determined by the condition of the storage element, strike the uorescent coating and produce luminescence for the area. Secondary electrons are also released and these are co1- lected by the metal portion of the target electrode 61 which therefore constitutes a detecting electrode. Electrode 6'! is therefore connected to a high potential source of the order of 1000 to 2000 volts, with respect to cathode. The electron current, if any, can be observed by a suitable indicator connected across the output load impedance or used in any manner desired. It will bev apparent that this form of construction for the second target electrode may be employed with any of the previously described first target electrodes in the general arrangement illustrated in Fig. 1.

A further important feature of the separation of the storage and indicating functions is now apparent. In the earlier copending application, Serial No. 720,876, iiled January 8, 1947, now Patent No. 2,442,985, issued June 8, 1948, describing the use of alight link to determine the condition' or" the storage element, it was necessary to provide a time delay after the standby condition was terminated. This was due to the fact that the fluorescent material was .deposited on the electrode corresponding to the present rst target electrode and produced luminescence for all elements which were at collector potential and under bombardment. The present system eliminates this time delay since the second target electrode carries the iluorescent material, and the positive potential need be applied to this electrode only when a reading is desired. Thus there need be no general luminescence during standby operation and the reading may be made instantly and accurately by energizing the second target electrode only when a reading is desired.

In certain applications of the storage tube, it is desired that it be operated at an extremely high speed. It is thus desirable that those elements which are to be charged to a potential have as low a capacity as possible. The second target electrodes illustrated in Figs. 'l and 9 are quite large and consequently inherently have a relatively large capacity to ground through the adjacent electrodes and other elements of the tube.

In order to reduce the capacity of the second target electrode and thus to increase the speed or response of the device, the arrangement illustrated in Fig. l may be employed. Only a portion of the device has been illustrated, that which is not shown being identical to the arrangement illustrated in Fig. 1, or any of its modincations. Thus, the rst target electrode 51 is shown in the form illustrated in Fig. 7, including an auxiliary electrode 80 which is biased to a potential of -50 volts. Three focusing electrodes 82, fili and 86 are positioned so as to enclose the area beyond the rst target electrode and biased so as to permit all electrons passing through the first target to move toward the second target electrode, which in this case is simply a ine vfire 8B. Focusing electrodes 82 and 84 are biased to a potential of approximately +100 volts, while focusing electrode 86 is biased to a potential of approximately -50 volts. As a result, any

electrons which pass through the iirst target electrode 5l are `directed toward and ultimately land on `the second target electrode 88 which is maintained at a high positive potential as inthe preceding cases. Some electrons may revolve manytimesaroundthe wire before being co1- lected, but this is-of no importance since electron transittimes are .no limitation in the operation ofthe device. i -f While the invention has been described in connection with a device embodying the rectangular structure illustrated in the preceding figures, the principle of operation by means of which the storage element acts asagrid to control the W of electrons to the.. second target electrode is applicable to cylindrical types of construction such as are illustrated inthe copending applicationv Serial No. 665,031. In such case the rst target electrode wouldconstitute a plurality of interconnected wiresy 'positioned either in the center or around the edges of the grid windows so as to intercept some `electrons and permit others to pass through. The gridr wires would then be coatedH-with a dielectric secondaryemissive material lin the manner employed in connection withA Fig. 6, for example. Certain electrons would then be directed to and impinge on the dielectric surface while others could pass between the wires onto kthe second target, depending upony the lestablished potential of the dielectric surface. The-second target would be a cylindrical member surrounding the entire electrode structure.

Since the numberl of electronslpassing through the first target electrode is but a small number of those directed toward the storage element, the output current will necessarily bevrather small. This may readily be-amplified within the device by substituting for the `second target electrode of Fig, 10, for example, the input of an electron multiplier device which may, if desired, be embodied within the tube structure. Alternatively, one or more electron lmultipliers may be positioned adjacent the aperture of the iirst target electrode. Sincemselection of the element whose condition is to be 4determined is accomplished by the grid network, a common electron multiplier channel may be employed for more than one element, and the output of all such devices may be connected in parallel.

What I claim is:

1. In an electron storage system, the combination of an electron discharge device comprising a source of electrons; rst and second target electrodes; a collector electrode adjacent said rst target electrode; electrodal means for directing electrons from said source toward one or more distinct elemental areas of said nrst target electrode; electrode means and an input connection therefor for charging said elemental areas to either one of two predetermined potentials, one of said potentials being cathode potential and the other being the potential of said collector electrode; each of said elemental areas having an aperture therethrough for permitting electrons to pass through a given elemental area of said nrst target electrode and strike said second target electrode when said elemental area is under electron bombardment and is at collector potential.

2. An electron discharge device including a cathode; one or more accelerating electrodes; first and second control grid networks; a collector electrode; and iirst and second target electrodes; said electrodes being positioned in the order named; said rst target electrode including a plurality of separate secondary-emis'sive storage elements and a capacityr'plate. in capacitive 4relation thereto, eachY element having an. aperture for the lpassage therethrough of. aiportionof the:

impinging electrons.

3.' A device of theicharacter described in claim2A toeither one of twowpreselected potentials, the

method of indicating torwhich of said potentials a given element is charged. which 'includes the steps of selecting' said element, bomb-arding the selected elementwith electrons'toltheV exclusion of other elements, establishing an electric field adjacent' said selectedv element to` cause ythe bombarding electrons to pass through said element when said element is charged to .one of saidfpreselected'potentials and to prevent said electrons from passing through said element when said element is charged to the other'oi:` said preselected potentials, and deriving from the electrons which pass through said element `an indication of its condition.

5. The method setV forth in claim 4 which includes the additional step of utilizing the electrons :passing through saidrselected element to produce a uorescent indication of the condition of said element.

6. A device Aof the character described in'claim 2 in which said rst target electrode comprises a perforated mica sheet, and aperforated metal plate adjacent thereto. f

'7. A device of the character ydescribed in claim 2 in which said first target electrodecomprises a perforated vmetallic plate having Athereon a layer of dielectric secondary-emissive material.

8. A device of-the character described in rclaim 2 in which said first target electrode comprises a perforated conductive Acapacity Vplate having Vlocated therein and insulated therefrom, a plural- 4 ity of sleeves of secondary-emissive-metal, one

12 of fsaid'sleevesflying in each elemental area 'of saidi electrode.

9..,A'nv electron discharge device comprising a source-.of electrons and a plurality of electrodes,

. at lleastsome of said electrodes comprising perforated;` sheets, means positioning said electrodes in' spaced, parallel relation with their perforations .inlregister for the passage of electrons therethrough; a' control grid network comprising a pluralityof .grid wires lying in a plane parallel tov ther :plane of said electrodes, said grid network being spaced between adjacent perforated sheets; anda-plurality' of insulating members supported in 'aligned aperturesY in said electrodes for supf. porting -said grid wires.

V10; vIn an electron storage system, the combination of` .an electron discharge device including a cathode; `one' or more accelerating electrodes; rstand second control grid networks; a collector. electrode; rst and second target electrodes; said electrodes being positioned in the order named; said iirst .target electrode including a plurality of separate secondary-emissive storage elements and a capacity plate in capacitive relation thereto, each element having an aperture Afor thepassage therethroughof portion of the impinging electrons, a selection circuitfconnected with said first and second controlgrid networks, a conditioning pulse input circuit coupled tothe capacity plate of said rst targetv electrode, and means providing a bias supply connection for said capacity plate for applying a `negative biasing potential thereto with respectvto' said cathode.

Y JAN A. RAJCHMAN.

REFERENCES CTED The following references are of record in the iile 'of' this patent:

UNITED STATES PATENTS Number Name Date 1,814,805 Hitchcock July 14, 1931 2,172,859 Toulon Sept. 12, 1939 2,348,216 Holshouser May 9, 1944 2,424,289 Snyder July 22, .1947 

